The present invention relates to a variable displacement pump adapted to supply working fluid.
U.S. Patent Application Publication No. 2010/226799 (corresponding to Japanese Patent Application Publication No. 2010-209718) discloses a previously-proposed variable displacement pump.
The variable displacement pump disclosed in this patent application is a so-called vane pump. In this technique, the variable displacement pump includes a first control oil chamber, a second control oil chamber and an electromagnetic changeover valve. The first control oil chamber and the second control oil chamber are formed radially outside a cam ring and separated from each other. The first control oil chamber receives a pump discharge pressure and thereby applies force to the cam ring in a direction that reduces an eccentricity amount of the cam ring whereas the second control oil chamber receives the pump discharge pressure and thereby applies force to the cam ring in a direction that increases the eccentricity amount of the cam ring. The electromagnetic changeover valve selectively supplies or discharges the pump discharge pressure to/from the second control oil chamber by ON-OFF control. That is, the pump discharge pressure is controlled to attain a low-pressure characteristic and a high-pressure characteristic by controllably increasing and reducing the eccentricity amount of the cam ring in accordance with rotational speed of the pump.